1. Field of the Invention
The invention relates to conversion devices for use in enabling chain stitches to be sewn on a lock stitch sewing machine.
2. Description of the Prior Art
Various conversion devices with which a lock stitch sewing machine is enabled to sew chain stitches can be found in the prior art. Such conversion devices commonly include a thread retaining post on which a loop cast off by a looptaker may be retained until the sewing needle has been stepped therethrough, mechanism for stripping the retained loop from the post, and a bobbin case insert for guiding the thread cast off the looptaker onto the post. A lock stitch conversion device as described may be found for example, in U.S. Pat. No. 4,278,037 for "Chain Stitch Conversion for Lock Stitch Sewing Machine" of Gerald J. Creed et al., issued July 14, 1981.
When chain stitches were to be formed on a lock stitch sewing machine fitted with a conversion device, it was necessary to thread the machine differently than for lock stitching. For chain stitching, the thread was passed through a special chain stitch eyelet or guide, effective to limit the quantity of thread supplied to the looptaker by a descending takeup, and so enable the loop-taker to pull loops stripped from the post of the conversion mechanism up to a piece of material being sewn for the setting of chain stitches by the takeup. However, it was easy for an operator to mistakenly thread the machine for lock stitching when it should have been threaded for chain stitching, and when switching from a chain stitching mode to a lock stitching mode to leave the machine threaded for chain stitching. In either event, faulty stitches were produced.
It is a prime object of the present invention to render a lock stitch sewing machine convertible for chain stitch sewing without the need for a special chain stitch guide or eyelet.
It is another object of the invention to provide a bobbin case insert which is effective on a lock stitch sewing machine to consume thread as required for the machine to form chain stitches.
Other objects and advantages of the invention will become apparent during a reading of the specification taken in connection with the accompanying drawings.